Several different types of indicating devices for providing a continuous visual indication of the degree of clogging with dirt and dust of a vacuum cleaner dust container are known. Usually the indicating device is acted upon by the pressure differential generated by the motor-fan unit of the apparatus, either between the inside, and the outside of the dust container, or between the outside of the dust container and atmospheric pressure. The device, often takes the shape of a piston, a diaphragm, or similar structure, and moves against the force of a spring, and its instantaneous position can be observed from the outside of the apparatus, and an indication of the degree of clogging of the dust container is thereby determined.
It should be evident that the spring characteristics and tension are selected so that for a motor having a certain output the end position of the movable means, such as a piston, signals that the dust container should be replaced. Such a device functions rather well in a vacuum cleaner motor having constant output but in vacuum apparatus having motor regulators where the output can be varied the conditions are no longer valid. As a consequence, under certain conditions, the indicator for the degree of clogging of the dust container gives a faulty indication. For instance, in case of partial motor output, this may result in a premature replacement of the dust container, which consequently entails an increase in the running costs of the vacuum cleaner. The indicator signals are therefore correct only for a certain position of the output regulator.
A principal object of the present inventon is to eliminate the foregoing disadvantage of prior art constructions and the invention is mainly characterized in that the vacuum cleaner, which has a motor regulator, is provided with a device for continuous varying of the tension of the spring against the force of which the means, such as a diaphragm, is movable.